Users of mobile electronic devices can communicate with one another on a variety of levels and using a variety of technologies. For example, presence service is a network service which accepts, stores and distributes presence information. Presence information may be a status indicator that conveys ability and willingness of a potential communication partner, a user for example, to communicate. A user may provide presence information via network connection to a presence service, which is stored in what constitutes his personal availability record and can be made available for distribution to subscribers to convey his availability for communication.
Presence information may have wide application in many communication services, including, for example, instant messaging and/or recent implementations of voice over IP. Presence service may be implemented in a single server or have an internal structure involving multiple servers and/or proxies. There may be complex patterns of redirection and proxying while retaining logical connectivity to a single presence service. Also presence service may be implemented as direct communication among users and subscribers, i.e. a server is not required.
Presence service may be implemented using, for example, sessions, which may be generally be described as either a lasting connection using the session layer of a network protocol or a lasting connection between a user and a peer, typically a server. A session may involve the exchange of many packets between the user's computer and the server. A session may be implemented as a layer in a network protocol using, for example, Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. Presence service may use icons that are preloaded on a device to indicate a personal presence, but, absent additional communication, may provide no additional information to a user or subscriber.